In the related art, in a manufacturing process of electronic components, various ultrasonic cleaning apparatuses using ultrasonic vibrations for cleaning surfaces of the electronic components as objects to be cleaned are proposed as means for removing dusts (particles) such as fine refuses or dirt adhered to the electronic components such as semiconductor wafers, hard disks, glass substrates.
As an example of the ultrasonic cleaning apparatus, there is an apparatus having a two-tank structure in which a cleaning tank includes an outer tank and an inner tank to be arranged in the outer tank. This apparatus has a configuration in which the inner tank formed of quartz or the like and the outer tank formed of metallic material such as stainless or resin material and provided with a transducer mounted thereon are provided for preventing adhesion of eluted metallic ion on the object to be cleaned when metal is used for the cleaning tank.
Also, medium liquid for propagating the ultrasonic vibrations generated by driving an ultrasonic transducer to cleaned member immersed in cleaning liquid stored in the inner tank is stored in the outer tank. The inner tank is arranged in the outer tank in a state in which a bottom plate thereof is soaked in the medium liquid. In the ultrasonic cleaning apparatus in the configuration as described above, the object to be cleaned immersed in the cleaning liquid in the inner tank is cleaned using the ultrasonic vibrations generated by oscillating the transducer by predetermined signals.
In order to generate the ultrasonic vibrations, signals of a single frequency or frequency modulated signals are generally used. The high-frequency signals of a single frequency are configured to provide signals of a constant frequency to the transducer to generate the ultrasonic vibrations.
The ultrasonic cleaning apparatuses in which the frequency modulated high-frequency signals are applied are disclosed in Patent Documents 1 and 2, although they are not the cleaning tanks having a two-tank structure as described above. FIG. 8 is a cross-sectional view of the ultrasonic cleaning apparatus in Patent Document 1 viewed from the front. An ultrasonic cleaning apparatus 301 includes a cleaning tank having a single tank structure having a bottom plate 307 on which a plurality of transducers 309 are fixed. It has a configuration to provide frequency modulated high-frequency signals at a predetermined modulation width to the respective transducers 309 in order to solve the variation in oscillating performance among the plurality of transducers 309.
Patent Document 2 is an ultrasonic cleaning apparatus having two oscillators for generating ultrasonic vibrations. The respective oscillators are configured to generate the ultrasonic vibrations at frequencies different from each other by frequency modulated high-frequency signals to solve nonuniformity of the sound pressure in the cleaning tank.
[Patent Document 1] JP-A-63-36534
[Patent Document 2] JP-A-8-131978